The objective of this proposal is to elucidate the role of viral proteins in the regulation of papovavirus (polyoma and SV40 replication. While others are studying the regulation of one round of synthesis we propose to study factors regulating the availability of newly synthesized DNA as template for further DNA synthesis. We have previously shown that pulse-labeled viral DNA is used as a template for DNA synthesis (re-enters replication) over a period of several hours and then is removed from the pool which is available for replication. The factor(s) responsible for this removal is unclear. In this study the kinetics of removal of progeny DNA from the pool which is available for replication will be compared to the kinetics of the progression of this DNA along the pathway to encapsidation. The effect of viral mutants on the kinetics of re-entry and on virus maturation will be examined. Such experiments will clarify the role of viral proteins and virus maturation in the regulation of viral replication. They will have direct bearing on the molecular nature of the virus-cell interaction which determines the outcome of infection (replication or transformation). They may also suggest ways that cellular DNA replication is regulated.